Existing ignition transformers are manufactured separately as single components and in a separate production process step before they are subsequently applied in igniter devices later.
Such an ignition transformer already has its full dielectric strength before its further production application. Its assembly mostly consists of a simple tube in which an insulated ferrite rod, carrying a secondary coil layer, is telescoped in. Then the primary coil windings subsequently will be applied on the outer surface of the tube.
Since air caverns could remain inside the assembly, especially between the tube and the secondary coil, and could be ionized which results in undesired losses, this interior space must be potted completely. As a side effect this avoids leakage currents and humidity.
Therefore this ignition transformer is sealed on its bottom and then filled up with encapsulating material from its top side.
Always a potting of the ignition transformer is mandatory, before it is assembled in a device.
Commonly ignition transformers have only one cylindrical or rod shaped ferrite core and therefore have an open non captured outer magnetic field. Rod shaped long coils with an open outer magnetic field have an undefined coupling in terms of an ideal transformer where the transmission ratio could be easily calculated.
Therefore at long rod ignition transformers it is advisable to understand the transformer as a sequential connection of small single transformer sections in series. Under this aspect it is mandatory to evenly distribute all primary ribbon turns as well as all secondary turns along the full size of the rod. This is a major difference to short segmented coil bobbin ignition transformers.
Unfortunately, therefore it is also mandatory to insulate the primary from the secondary windings of the transformer over the full length.
Besides adequate insulation it also must be paid attention to avoid any remaining ionizable air regions between the primary and secondary coil. If the ignition transformer is constructed by means of coil formers the space between secondary winding and coil former must be filled with a liquid, which later will gelatinise or harden.
So far known tube similar coil formers had been used for long rod coils with very small space between tube inner diameter and secondary winding outer diameter. The filling with pasty potting material to displace air with subsequently hardening could only be achieved with corresponding difficulty. Correspondingly ignition transformers with small outer diameter could only be produced with difficulty.
Assignment of this invention is the improved method of manufacturing of a long rod shaped ignition transformer with small diameter.
The method is based on a coil former with a primary outer winding of an ignition transformer which is open on one side along its full length or which is also equipped with channel openings at different sides or places. Thus the penetration of the potting material into the inner sections of long ignition transformers is strongly simplified. In contrast to the cylinder form of the ferrite rod, the coil bobbin, or better, the coil carrier must not necessarily be symmetric as at or at the opened sides of the profile, a high voltage proof insulation is not provided by the coil carrier alone, but instead is provided later in interaction with the highly insulating properties of the potting material.
At the open side respectively through the openings of the coil carrier potting mass is penetrating in the inside of the ignition transformer using the interstices of the primary winding coil turns and the open side of the carrier. The ignition transformer obtains its required dielectric strength later after the common potting process inside the igniter unit case.
Without problems the encapsulating mass can penetrate through the interstices of the primary turns, because the primary winding consists of some large turn to turn spaces which are evenly distributed over a relatively large length of the ignition transformer. Even if a substantially wider flat conductive ribbon is used, there is always sufficient interstice to fill the ignition transformer without problems.
As the circuitry to drive the ignition transformer mostly as one unit has to be potted also, a major production step can be saved if the ignition transformer with its at least one open sided coil carrier is potted in combination with the ignition circuitry as a functional unit in one final process step.
By this method when the ignition transformer is potted together with the circuitry as a component within an igniter case, the coil carrier can be used to hold the inner wound ferrite rod and to fix the outer primary winding. The carrier can be kept simple, e.g. may exist just as a simple U profile. Here it does not matter if this is a rounded or a cornered U profile.
At this manufacturing step of the method attention has to be paid, so that the distance between the primary and the secondary windings at the open parts or ends of the profile is kept sufficiently large that the potting material can provide enough insulation and there is no danger of a direct contact or short due to accidental deforming caused by unwanted touching during assembly.
It will be very helpful if the ferrite rod, wound with the secondary spiral winding of the ignition transformer, is fixed inside with glue mass at the bottom side (opposite to the open side) of the U profile coil carrier. By this means getting out of place can be avoided, and in addition potting through the openings oriented to the sides is further improved.